Introduction to Data Communication 2007
Exercises 5 (19.4.)
What kind of IP packets does A send? What does the router do to
these packets? What kind of IP packets does B receive? Give the
contents of the IP header fields involved in fragmentation in the
sent and received IP packets.
Give, based on the routes found, the routing table for node
A. In the routing table there is, for each node the outlink to be
used and the cost of the route. The outlinks are numbered so that
the link from A to be is number 1, from A to D number 2 and from A
to C number 3.
With a program called traceroute you can find out
what routes packets really travel in the Internet. Links to many
traceroute services are to be found from the net address
http://www.traceroute.org, for example the traceroute service of Funet http://www.csc.fi/cgi-bin/nph-traceroute
or the traceroute service of ETSI
http://portal.etsi.org/webstats/traceroute.asp. Find out how packets are routed from USA or Canada to
the Computer Science Department at the University of Helsinki (cs.helsinki.fi)
or some other domain or IP address
chosen by you.
What information do you get about the routes?
How is the traceroute program really working to get that information?
Consider a datagram networks using 32-bit host addresses. Suppose a router has four links,
numbered 0 through 3, and packets are to be forwarded to the link interface as follows:
Destination Address Range Link interface
11100000 00000000 00000000 00000000
............. 0
11100000 11111111 11111111 11111111
11100001 00000000 00000000 00000000
............ 1
11100001 00000000 11111111 11111111
11100001 00000001 00000000 00000000
........... 2
11100001 11111111 11111111 11111111
otherwise 3
11001000 10010001 01010001 01010101
11100001 00000000 11000011 00111100
11100001 10000000 00010001 01110111
Consider a router that interconnects three subnets: Sub1, Sub2, and Sub3. Suppose
all of the intefaces in each of these three subnets are required to have the prefix 223.1.17.0/24. Also suppose that Sub1 is required to support up to 125 interfaces, and Sub2 and Sub3 are each required to support up to 60 interfaces. Provide three network addresss (of form a.b.c-d/x) that satisfy these contraints.
The network layer of host A gets from its transport layer
3000 bytes of data to be sent to the host B. A and B are situated in
different networks that are connected by one router. A's LAN can
carry at most 1500 bytes of data in one packet and the maximum size
of data in B's LAN is only 1000 bytes. Suppose that the next
sequence number for A's IP packet is 100.
A - XXXXXXXXX - router - XXXXXXXXXXXX - B
LAN a LAN b
max. 1500 bytes data max. 1000 bytes data
A ---------------B
| / |
| / |
| / |
| / |
| / |
| / |
| E |
| / \ |
| / \ |
| / \ |
| / \ |
| / \ |
| / \|
C -------------- D
3
B . . . . . . .F
. . . .
. . . .
3 . 1 . 4 . . 2
. . . .
. 3 . . 3 .
network A . . . . . . . D . . . . . . . .E
. . . .
. . . .
. . 2 . 2 .
2 . . . . 1
. . . .
. . . .
C . . . . . . . G
2